I'm only going to critique your colouring instead of the actual drawing, k?

The colours looks kinda bold for some reason, maybe from the lack of shading.The only thing I see you did for 'shading' is put a shine on the dress and on the hair.You should make the shine more transparent and add in more shading, maybe add in small highlights in the hair.It looks like you used the Magic Wand tool and then filled in the colours and there are small white bits in a few places, looking at the small fold lines on the dress. That have whites around them.

You should make new layers under the lineart and make different layers for the different colours. Colour freely and rub out any bits that goes out of place. Do NOT use the magic tool unless your brush is an actual pen tool (SAI). Here's an example of an old random drawing I did:

May stretch page:

I know this is Photoshop, but I assume you can do the same on SAI, unless I'm wrong.Sorry if any of my critique or advice is innaccurate.